Methods for the detection of soluble β-amyloid peptide

ABSTRACT

Soluble β-amyloid peptide (βAP) is measured in biological fluids at very low concentrations, typically in the range from 0.1 ng/ml to 10 ng/ml. The measurement of βAP concentrations in animals or conditioned medium from cultured cells can be used for drug screening, where test compounds are administered to the animals or exposed to the cultured cells and the accumulation of βAP in the animal or culture medium observed. It has been found that elevated levels of βAP in body fluids, such as blood and cerebrospinal fluid, is associated with the presence of a βAP-related condition in a patient, such as Alzheimer&#39;s Disease. Methods for diagnosing and monitoring βAP-related conditions comprise measuring the levels of βAP in such body fluids from a patient.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of Ser. No. 07/965,972, filed Oct. 26, 1992, nowabandoned; which is a continuation in part of Ser. No. 07/911,647, filedJul. 10, 1992, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to methods and compositions fordetecting soluble β-amyloid peptide (βAP) in fluid samples. Moreparticularly, the present invention relates to screening methods for theidentification of inhibitors of βAP production where βAP is detected invitro or in vivo and to diagnostic methods where βAP is detected inpatient samples.

Alzheimer's Disease (AD) is a degenerative brain disorder characterizedclinically by progressive loss of memory, cognition, reasoning, judgmentand emotional stability that gradually leads to profound mentaldeterioration and ultimately death. AD is a very common cause ofprogressive mental failure (dementia) in aged humans and is believed torepresent the fourth most common medical cause of death in the UnitedStates. AD has been observed in races and ethnic groups worldwide andpresents a major present and future public health problem. The diseaseis currently estimated to affect about two to three million individualsin the United States alone. AD is at present incurable. No treatmentthat effectively prevents AD or reverses its symptoms and course iscurrently known.

The brains of individuals with AD exhibit characteristic lesions termedsenile (or amyloid) plaques, amyloid angiopathy (amyloid deposits inblood vessels) and neurofibrillary tangles. Large numbers of theselesions, particularly amyloid plaques and neurofibrillary tangles, aregenerally found in several areas of the human brain important for memoryand cognitive function in patients with AD. Smaller numbers of theselesions in a more restricted anatomical distribution are also found inthe brains of most aged humans who do not have clinical AD. Amyloidplaques and amyloid angiopathy also characterize the brains ofindividuals with Trisomy 21 (Down's Syndrome) and Hereditary CerebralHemorrhage with Amyloidosis of the Dutch-Type (HCHWA-D). At present, adefinitive diagnosis of AD usually requires observing the aforementionedlesions in the brain tissue of patients who have died with the diseaseor, rarely, in small biopsied samples of brain tissue taken during aninvasive neurosurgical procedure.

The principal chemical constituent of the amyloid plaques and vascularamyloid deposits (amyloid angiopathy) characteristic of AD and the otherdisorders mentioned above is an approximately 4.2 kilodalton (kD)protein of about 39-43 amino acids designated the β-amyloid peptide(βAP) or sometimes Aβ, AβP or β/A4. βAP was first purified and a partialamino acid sequence reported in Glenner and Wong (1984) Biochem.Biophys. Res. Commun. 120:885-890. The isolation procedure and thesequence data for the first 28 amino acids are described in U.S. Pat.No. 4,666,829.

Molecular biological and protein chemical analyses conducted during thelast six years have shown that βAP is a small fragment of a much largerprecursor protein, referred to as the β-amyloid precursor protein (APP),that is normally produced by cells in many tissues of various animals,including humans. Knowledge of the structure of the gene encoding APPhas demonstrated that βAP arises as a peptide fragment that is cleavedfrom APP by as-yet-unknown enzymes (proteases). The precise biochemicalmechanism by which the βAP fragment is cleaved from APP and subsequentlydeposited as amyloid plaques in the cerebral tissue and in the walls ofcerebral and meningeal blood vessels is currently unknown.

Several lines of evidence indicate that progressive cerebral depositionof βAP plays a seminal role in the pathogenesis of AD and can precedecognitive symptoms by years or decades (for review, see Selkoe (1991)Neuron 6:487). The single most important line of evidence is thediscovery in 1991 that missense DNA mutations at amino acid 717 of the770-amino acid isoform of APP can be found in affected members but notunaffected members of several families with a genetically determined(familial) form of AD (Goate et al. (1991) Nature 349:704-706; ChartierHarlan et al. (1991) Nature 353:844-846; and Murrell et al. (1991)Science 254:97-99) and is referred to as the Swedish variant. A doublemutation changing lysine⁵⁹⁵ -methionine⁵⁹⁶ to asparagine⁵⁹⁵ -leucine⁵⁹⁶(with reference to the 695 isoform) found in a Swedish family wasreported in 1992 (Mullan et al. (1992) Nature Genet 1:345-347). Geneticlinkage analyses have demonstrated that these mutations, as well ascertain other mutations in the APP gene, are the specific molecularcause of AD in the affected members of such families. In addition, amutation at amino acid 693 of the 770-amino acid isoform of APP has beenidentified as the cause of the βAP deposition disease, HCHWA-D, and achange from alanine to glycine at amino acid 692 appears to cause aphenotype that resembles AD in some patients but HCHWA-D in others. Thediscovery of these and other mutations in APP in genetically based casesof AD proves that alteration of APP and subsequent deposition of its βAPfragment can cause AD.

Despite the progress which has been made in understanding the underlyingmechanisms of AD and other βAP-related diseases, there remains a need todevelop methods and compositions for diagnosis and treatment of thedisease(s). Treatment methods could advantageously be based on drugswhich are capable of inhibiting the generation of βAP in vivo. Toidentify such drugs, it would be desirable to provide screening assaysfor potential drugs which can inhibit βAP generation in in vivo and invitro models. It would be further desirable to provide methods andcompositions for diagnosis of βAP-related conditions, where thediagnosis is based on detection of βAP in patient fluid samples.Specific assays for βAP detection should be capable of detecting βAP influid samples at very low concentrations as well as distinguishingbetween βAP and other fragments of APP which may be present in thesample.

2. Description of the Background Art

Glenner and Wong (1984) Biochem. Biophys. Res. Comanun. 120:885-890 andU.S. Pat. No. 4,666,829, are discussed above. The '829 patent suggeststhe use of an antibody to the 28 amino acid βAP fragment to detect"Alzheimer's Amyloid Polypeptide" in a patient sample and diagnose AD.No data demonstrating detection or diagnosis are presented.

Numerous biochemical electron microscopic and immunochemical studieshave reported that βAP is highly insoluble in physiologic solutions atnormal pH. See, for example, Glenner and Wong (1984) Biochem. Biophys.Res. Commun. 122:1131-1135; Masters et al. (1985) Proc. Natl. Acad. Sci.USA 82:4245-4249; Selkoe etal. (1986) J. Neurochem. 46:1820-1834;Joachim et al. (1988) Brain Research 474:100-111; Hilbich et al. (1991)J. Mol. Biol. 218:149-163; Barrow and Zagorski (1991) Science253:179-182; and Burdick et al. (1992) J. Biol. Chem. 267:546-554.Furthermore, this insolubility was predicted by and is consistent withthe amino acid sequence of βAP which includes a stretch of hydrophobicamino acids that constitutes part of the region that anchors the parentprotein (APP) in the lipid membranes of cells. Hydrophobic,lipid-anchoring proteins such as βAP are predicted to remain associatedwith cellular membranes or membrane fragments and thus not be present inphysiologic extracellular fluids. The aforementioned studies and manyothers have reported the insolubility in physiologic solution of nativeβAP purified from AD brain amyloid deposits or of synthetic peptidescontaining the βAP sequence. The extraction of βAP from cerebral amyloiddeposits and its subsequent solubilization has required the use ofstrong, non-physiologic solvents and denaturants. Physiologic, bufferedsalt solutions that mimic the extracellular fluids of human tissues haveuniformly failed to solubilize βAP.

Separate attempts to detect APP or fragments thereof in plasma or CSFhave also been undertaken. A large secreted fragment of APP that doesnot contain the intact βAP region has been found in human cerebrospinalfluid (Palmerr et al. (1989) Proc. Natl. Acad. Sci. USA 86:6338-6342;Weidemann et al. (1989) Cell 57:115-126; Henriksson et al. (1991) J.Neurochem. 6:1037-1042; and Palmert et al. (1990) Neurology40:1028-1034); and plasma (Podlisny et al. (1990) Biochem. Biophys. Res.Commun. 167:1094-1101). The detection of fragments of thecarboxy-terminal portion of APP in plasma has also been reported (Rumbleet al. (1989) N. Engl. J. Med 320:1446-1452) as has the failure todetect such fragments (Schlossmacher et al. (1992) Neurobiol. Aging13:421-434).

Despite the apparent insolubility of native and synthetic βAP, it hasbeen speculated that βAP could occur in body fluids, such ascerebrospinal fluid (CSF) or plasma (Wong et al. (1985) Proc. Natl.Acad. Sci. USA 92:8729-8732; Selkoe (1986) Neurobiol. Aging 7:425-432;Pardridge et al. (1987) Biochem. Biophys. Res. Commun. 145:241-248;Joachim et al. (1989) Nature 341:226-230; Selkoe et al. (1989)Neurobiol. Aging 10:387-395).

Several attempts to measure βAP in CSF and plasma have been reported byboth radioimmunoassay methods (Pardridge et al. (1987) Biochem. Biophys.Res. Commun., supra, and WO90/12870 published Nov. 1, 1990) and sandwichELISAs (Wisniewski in Alzheimer's Disease, eds. Becker and Giacobini,Taylor and Francas, N.Y. pg. 206, 1990; Kim and Wisniewski in Techniquesin Diagnostic Pathology, eds. Bullock et al., Academic Press, Boston pg.106; and WO90/12871 published Nov. 1, 1990). While these reportsdetected very low levels of βAP immunoreactivity in bodily fluids,attempts to directly purify and characterize this immunoreactivityfurther and determine whether it represented SAP were not pursued, andthe efforts were abandoned. The possibility of βAP production bycultured cells was neither considered nor demonstrated. Retrospectively,the inability to readily detect βAP in bodily fluids was likely due tothe presence of amyloid precursor fragments with overlapping regions orfragments of βAP that obscured measurements and to the lack ofantibodies completely specific for intact βAP. In fact, the previousfindings by both Pardridge et al. and Kim et al. reported levels of βAPfour-to-fivefold lower than that shown in the present invention. This ispresumably because the antibodies used by both groups would crossreactwith other APP fragments containing part of βAP known to be present inCSF thereby interfering with the measurement, if any, of intact βAP. Thepresent invention overcomes these difficulties with the use ofmonoclonal antibodies specific to an epitope in the central junctionregion of intact βAP.

EP 444,856 provides a means of diagnosing Alzheimer's disease using asandwich immunoassay to "Alzheimer's Disease Associated Protein" (ADAP).ADAP is defined as a material reactive with the monoclonal antibodytermed Alz50, originally described by Wolozin et al. (1986) Science232:648-650. Alz50 has more recently been shown to react specificallywith phosphorylated forms of tau (Ksiezak-Reder et al. (1988) J. Biol.Chem. 263:7943-7947; Ueda et al. (1990) J. Neuroscience 10:3295-3304;Lee et al. (1991) Science 251:675-678). Hence, ADAPs representphosphorylated forms of tau and are unrelated to the amyloid precursorprotein of βAP described in this invention.

SUMMARY OF THE INVENTION

The present invention provides methods and compositions useful for theidentification of β-amyloid peptide (βAP) production inhibitors as wellas for the diagnosis and monitoring of βAP-related conditions inpatients, where the methods and compositions rely on the specificdetection of soluble βAP and/or βAP fragments in fluid samples. For theidentification of βAP production inhibitors, a test compound isintroduced to an in vitro or in vivo βAP generation model, and theeffect of the test compound on the amount of soluble βAP or βAP fragmentgenerated by the model is observed. Particularly useful as an in vitromodel are cell lines which express APP variants which overproduce βAP.Test substances which affect the production of βAP and/or βAP fragments,usually by reducing the amount produced, are considered to be likelycandidates for further testing for use as therapeutic drugs in thetreatment of βAP-related conditions, particularly Alzheimer's Disease.For the diagnosis and monitoring of βAP-related conditions, the amountof soluble βAP and/or βAP fragments in a patient sample, such as blood,cerebrospinal fluid (CSF), urine, or peritoneal fluid, is measured andcompared with a predetermined control value, such as a normal value (inthe case of diagnosis) or a prior patient value (in the case ofmonitoring).

In a particular aspect, the present invention provides specific bindingassays which are useful for the measurement of βAP concentrations influid samples and which may be employed in both the drug screening andpatient diagnostic and monitoring methods just described. The specificbinding assay of the present invention is capable of detecting solubleβAP at the very low concentrations which are characteristic of thepatient fluids and conditioned culture media, typically being capable ofmeasuring threshold concentrations in the range from about 1 ng/ml to 10ng/ml, or lower.

Specific binding assays according to the present invention employ atleast one binding substance specific for an epitope or determinant siteon the βAP molecule, which site is generally not found on otherfragments or degradation products of the β-amyloid precursor protein(APP). Particularly useful are antibodies which recognize a junctionregion within βAP, where the junction region is located about the siteof normal proteolytic cleavage of APP between residues Lys¹⁶ and Leu¹⁷(Esch et al. (1990) Science 248:1122-1124 and Anderson et al. (1991)Neuro. Science Lett. 128:126-128), typically spanning amino acidresidues 13 and 28. Exemplary specific binding assays include two-site(sandwich) assays in which the capture antibody is specific for thejunction region of βAP, as just described, and a labeled second antibodyis specific for an epitope other than the epitope recognized by thecapture antibody. Particularly useful are second antibodies which bindto the amino-terminal end of βAP, typically recognizing an epitopewithin amino acid residues 1-16.

In another aspect, the present invention provides a system for detectingsoluble βAP in a fluid sample. The system includes a first bindingsubstance, typically an antibody, specific for an epitope in a junctionregion of βAP, as described above, and a second binding substance,typically an antibody, specific for an epitope of βAP other than theepitope bound by the first binding substance. One of the first andsecond binding substances is bound to a solid phase, while the other islabeled, with the first binding substance preferably being a captureantibody bound to a solid phase and the second binding substancepreferably being a labeled antibody, more preferably being anenzyme-labeled antibody. The system may further include substrate forthe enzyme, the system is useful in performing enzyme-linkedimmunosorbent assays (ELISA) having high specificity and sensitivity forthe detection of βAP in fluid samples.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph illustrating the detection of three synthetic βAPpeptides using an ELISA assay format with monoclonal antibody 266 as thecapture antibody and monoclonal antibody 10D5 as the reporter antibody.Antibody 266 was prepared against a synthetic peptide including aminoacid residues 13-28 of βAP- Antibody 10D5 was raised against a syntheticpeptide including amino acid residues 1-28 of βAP.

FIGS. 2A and 2B are charts comparing the plasma and CSF concentrationsof βAP in normal control and AD patients.

FIG. 3 is a chart comparing the CSF concentration of βAP in normalcontrols (C), Alzheimer's Disease patients (AD), cerebral vascularaccident (CVA) patients (stroke), and Parkinson's Disease (PD) patients.

FIG. 4 is a Western blot of affinity-purified conditioned media from acell line which overexpresses APP. The affinity-purified material fromthe conditioned media of human mixed-brain cell cultures which had beenfurther purified by reversed-phase chromatography.

FIG. 5 is an autoradiogram demonstrating the presence of soluble βAP inthe culture fluid of human kidney 293 cells. The βAP wasimmunoprecipitated from the culture fluid with a βAP-specific antibodyto residues 1-40 of βAP.

FIG. 6 is an autoradiogram demonstrating that βAP in the media of humankidney 293 cells is fully soluble and that it remains in the post-10⁵ xgsupernatant and is not found in the post-10⁵ xg pellet afterultracentrifugation.

FIG. 7 shows the quantitation of βAP (left panel) and the secretedβ-amyloid precursor protein (APPs) (right panel) in conditioned media intransiently transfected 293 cells using two distinct sandwich ELISAs.Each column represents the mean of four transfection experiments withnormal or variant APP constructs with the exception of the mock column,which is based on three transfection experiments.

FIG. 8 is an autoradiogram demonstrating the levels of soluble βAP inthe culture fluid of human kidney 293 cells transfected with normal orvariant APP₆₉₅ constructs.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

The present invention results from the discovery that detectable amountsof soluble β-amyloid peptide (βAP) and βAP fragments are generatedcontinuously at low concentrations by a wide variety of mammalian cells.In particular, it has been found that such βAP peptides are generated invitro by cultured mammalian cells and may be measured in the conditionedculture medium of numerous mammalian cell lines. It has been furtherfound that βAP peptides are present in the body fluids of variousmammalian hosts, and that elevated levels of βAP peptides are associatedwith βAP-related conditions, such as Alzheimer's Disease and Down'sSyndrome.

Based on this discovery, the present invention provides both methods fordrug screening to identify potential βAP generation inhibitors andmethods for diagnosing and monitoring βAP-related conditions. Bothmethods rely on the measurement of very low βAP concentrations in afluid sample, typically in the range from 0.1 ng/ml to 10 ng/ml, withthe present invention further providing highly sensitive and specificmethods for performing such measurements. In particular, detectionmethods of the present invention provide for measurement of βAP atthreshold concentrations of 0.1 ng/ml and below, and are sufficientlyspecific to distinguish βAP from other fragments of the β-amyloidprecursor protein (APP) which contain precursor amino acids in additionto the 39-43 amino acids that comprise the βAP region.

The mechanism of βAP and βAP fragment generation is not presentlyunderstood. It is possible that intact or full length βAP is producedintracellularly and thereafter released or secreted into theextracellular fluid, i.e., body fluids in vivo and conditioned cellculture medium in vitro. Alternatively, it is possible that a precursorprotein or fragment, which may be the entire APP or a portion thereofcontaining the βAP region, is secreted or released from the mammaliancells and processed outside of the cellular source. Regardless of theparticular mechanism, the present invention relies on the detection andmeasurement of the concentrations or amounts of βAP and βAP fragments inextracellular fluids, including conditioned culture medium and bodyfluids, as discussed in more detail below.

The term "β-amyloid peptide" (βAP) as used herein refers to anapproximately 4.2 kD protein which, in the brains of AD, Down'sSyndrome, HCHWA-D and some normal aged subjects, forms the subunit ofthe amyloid filaments comprising the senile (amyloid) plaques and theamyloid deposits in small cerebral and meningeal blood vessels (amyloidangiopathy). βAP can occur in a filamentous polymeric form (in thisform, it exhibits the Congo-red and thioflavin-S dye-bindingcharacteristics of amyloid described in connection therewith). βAP canalso occur in a non-filamentous form ("preamyloid" or "amorphous" or"diffuse" deposits) in tissue, in which form no detectable birefringentstaining by Congo red occurs. A portion of this protein in the insolubleform obtained from meningeal blood vessels is described in U.S. Pat. No.4,666,829. βAP when used in connection with this invention, specificallyrefers to an approximately 39-43 amino acid peptide that issubstantially homologous to the form of the protein produced by themethod described in the patent of Glenner et al., but which, accordingto the instant invention, can be found in and purified from theextracellular fluid (medium) of cultured cells grown in vitro or frombody fluids of humans and other mammals, including both normalindividuals and individuals suffering from βAP-related conditions. Thus,βAP also refers to related βAP sequences that result from mutations inthe βAP region of the normal gene. In whatever form, βAP is anapproximately 39-43 amino acid fragment of a large membrane-spanningglycoprotein, referred to as the β-amyloid precursor protein (APP),encoded by a gene on the long arm of human chromosome 21. βAP is furthercharacterized by its relative mobility in SDS-polyacrylamide gelelectrophoresis or in high performance liquid chromatography (HPLC). Its43-amino acid sequence is: ##STR1## or a sequence that is substantiallyhomologous thereto.

The term "βAP peptides" as used herein refers to intact or full lengthβAP as well as to fragments and degradation products of βAP which aregenerated at low concentrations by mammalian cells. Particular βAPfragments have a molecular weight of approximately 3 kD and arepresently believed to consist of amino acid residues 11-40 and 17-40 ofβAP.

The term "βAP junction region" as used herein refers to a region of βAPwhich is centered at the site between amino acid residues 16 and 17(Lys¹⁶ and Leu¹⁷) which is a target for normal proteolytic processing ofAPP. Such normal processing results in a variety of APP fragments whichare potentially immunologically cross-reactive with the intact βAPmolecule and fragments of βAP which are to be identified in the methodsof the present invention. The junction region will span amino acidresidues 10 to 35, preferably spanning amino acid residues 15 to 30,with antibodies raised against a synthetic peptide consisting of aminoacid residues 13-28 having been found to display the requisitespecificity.

The term "β-amyloid precursor protein" (APP) as used herein is definedas a polypeptide that is encoded by a gene of the same name localized inhumans on the long arm of chromosome 21 and that includes βAP within itscarboxyl third. APP is a glycosylated, single-membrane-spanning proteinexpressed in a wide variety of cells in many mammalian tissues. Examplesof specific isotypes of APP which are currently known to exist in humansare the 695-amino acid polypeptide described by Kang et al. (1987)Nature 325:733-736 which is designated as the "normal" APP; the751-amino acid polypeptide described by Ponte et al. (1988) Nature331:525-527 (1988) and Tanzi et al. (1988) Nature 331:528-530; and the770-amino acid polypeptide described by Kitaguchi et al. (1988) Nature331:530-532. Examples of specific variants of APP include pointmutations which can differ in both position and phenotype (for review ofknown variant mutations see Hardy (1992) Nature Genet. 1:233-234).

The term "APP fragments" as used herein refers to fragments of APP otherthan those which consist solely of βAP or βAP fragments. That is, APPfragments will include amino acid sequences of APP in addition to thosewhich form intact βAP or a fragment of βAP.

The term "βAP-related condition" as used herein is defined as includingAlzheimer's Disease (which includes familial Alzheimer's Disease),Down's Syndrome, HCHWA-D, and advanced aging of the brain.

The terms "conditioned culture medium" and "culture medium" as usedherein refer to the aqueous extracellular fluid which surrounds cellsgrown in tissue culture (in vitro) and which contains, among otherconstituents, proteins and peptides secreted by the cells.

The term "body fluid" as used herein refers to those fluids of amammalian host which will be expected to contain measurable amounts ofβAP and βAP fragments, specifically including blood, cerebrospinal fluid(CSF), urine, and peritoneal fluid. The term "blood" refers to wholeblood, as well as blood plasma and serum.

According to the present invention, βAP and βAP fragments may bedetected and/or measured in a variety of biological and physiologicalsamples, including in vitro samples, such as conditioned medium fromcultured cells, including transfected cell lines and endogenous celllines, and in vivo patient samples, typically body fluids. Detection andmeasurement of βAP peptides may be accomplished by any technique capableof distinguishing βAP and βAP fragments from other APP fragments whichmight be found in the sample. Conveniently, immunological detectiontechniques may be employed using binding substances specific for βAP,such as antibodies, antibody fragments, recombinant antibodies, and thelike, which bind with specificity and sensitivity to βAP. In particular,it has been found that antibodies which are monospecific for thejunction region of βAP are capable of distinguishing βAP from other APPfragments. The junction region of βAP is centered at amino acid residues16 and 17, typically spanning amino acid residues 13-28, and suchjunction-specific antibodies may be prepared using synthetic peptideshaving that sequence as an immunogen. Particularly suitable detectiontechniques include ELISA, Western blotting, radioimmunoassay, and thelike.

A preferred immunoassay technique is a two-site or "sandwich" assayemploying a junction-specific antibody as the capture antibody (bound toa solid phase) and a second labeled antibody which binds to an epitopeother than that bound to by the capture antibody. The second labeledantibody preferably recognizes the amino terminus of βAP and may beconveniently raised against a synthetic peptide consisting essentiallyof amino acid residues 1-16 of βAP. Particular methods for preparingsuch antibodies and utilizing such antibodies in an exemplary ELISA areset forth in the Experimental section hereinafter.

Other non-immunologic techniques for detecting βAP and βAP fragmentswhich do not require the use of βAP specific antibodies may also beemployed. For example, two-dimensional gel electrophoresis may beemployed to separate closely related soluble proteins present in a fluidsample. Antibodies which are cross-reactive with many fragments of APP,including βAP, may then be used to probe the gels, with the presence ofβAP being identified based on its precise position on the gel. In thecase of cultured cells, the cellular proteins may be metabolicallylabeled and separated by SDS-polyacrylamide gel electrophoresis,optionally employing immunoprecipitation as an initial separation step.A specific example of the latter approach is described in theExperimental section hereinafter.

Antibodies specific for the βAP may be prepared against a suitableantigen or hapten comprising the desired target epitope, such as thejunction region consisting of amino acid residues 13-28 and the aminoterminus consisting of amino acid residues 1-16. Conveniently, syntheticpeptides may be prepared by conventional solid phase techniques, coupledto a suitable immunogen, and used to prepare antisera or monoclonalantibodies by conventional techniques. Suitable peptide haptens willusually comprise at least five contiguous residues within βAP and mayinclude more than six residues.

Synthetic polypeptide haptens may be produced by the well-knownMerrifield solid-phase synthesis technique in which amino acids aresequentially added to a growing chain (Merrifield (1963) J. Am. Chem.Soc. 85:2149-2156). The amino acid sequences may be based on thesequence of βAP set forth above.

Once a sufficient quantity of polypeptide hapten has been obtained, itmay be conjugated to a suitable immunogenic carrier, such as serumalbumin, keyhole limpet hemocyanin, or other suitable protein carriers,as generally described in Hudson and Hay, Practical Immunology,Blackwell Scientific Publications, Oxford, Chapter 1.3, 1980, thedisclosure of which is incorporated herein by reference. An exemplaryimmunogenic carrier utilized in the examples provided below is α-CD3εantibody (Boehringer-Mannheim, Clone No. 145-2C11).

Once a sufficient quantity of the immunogen has been obtained,antibodies specific for the desired epitope may be produced by in vitroor in vivo techniques. In vitro techniques involve exposure oflymphocytes to the immunogens, while in vivo techniques require theinjection of the immunogens into a suitable vertebrate host. Suitablevertebrate hosts are non-human, including mice, rats, rabbits, sheep,goats, and the like. Immunogens are injected into the animal accordingto a predetermined schedule, and the animals are periodically bled, withsuccessive bleeds having improved titer and specificity. The injectionsmay be made intramuscularly, intraperitoneally, subcutaneously, or thelike, and an adjuvant, such as incomplete Freund's adjuvant, may beemployed.

If desired, monoclonal antibodies can be obtained by preparingimmortalized cell lines capable of producing antibodies having desiredspecificity. Such immortalized cell lines may be produced in a varietyof ways. Conveniently, a small vertebrate, such as a mouse ishyperimmunized with the desired immunogen by the method just described.The vertebrate is then killed, usually several days after the finalimmunization, the spleen cells removed, and the spleen cellsimmortalized. The manner of immortalization is not critical. Presently,the most common technique is fusion with a myeloma cell fusion partner,as first described by Kohler and Milstein (1975) Nature 256:495-497.Other techniques including EBV transformation, transformation with bareDNA, e.g., oncogenes, retroviruses, etc., or any other method whichprovides for stable maintenance of the cell line and production ofmonoclonal antibodies. Specific techniques for preparing monoclonalantibodies are described in Antibodies: A Laboratory Manual, Harlow andLane, eds., Cold Spring Harbor Laboratory, 1988, the full disclosure ofwhich is incorporated herein by reference.

In addition to monoclonal antibodies and polyclonal antibodies(antisera), the detection techniques of the present invention will alsobe able to use antibody fragments, such as F(ab), Fv, V_(L), V_(H), andother fragments. In the use of polyclonal antibodies, however, it may benecessary to adsorb the anti-sera against the target epitopes in orderto produce a monospecific antibody population. It will also be possibleto employ recombinantly produced antibodies (immunoglobulins) andvariations thereof as now well described in the patent and scientificliterature. See, for example, EPO 8430268.0; EPO 85102665.8; EPO85305604.2; PCT/GB 85/00392; EPO 85115311.4; PCT/US86/002269; andJapanese application 85239543, the disclosures of which are incorporatedherein by reference. It would also be possible to prepare otherrecombinant proteins which would mimic the binding specificity ofantibodies prepared as just described.

In vivo detection of βAP in patient samples can be used for diagnosingand monitoring of Alzheimer's Disease and other βAP-related conditions,such as Down's Syndrome and HCHWA-D. Suitable patient samples includebody fluids, such as blood, CSF, urine, and peritoneal fluid. Thepresence of the βAP-related condition will generally be associated withelevated levels of βAP in the fluid when compared to those values innormal individuals, i.e., individuals not suffering from Alzheimer'sDisease or any other βAP-related condition. Diagnostic concentrations ofβAP in blood are in the range from 0.1 ng/ml to 10 ng/ml or higher, moregenerally 0.1 ng/ml to 3 ng/ml. Diagnostic concentrations of βAP in CSFare in the range from 0.1 ng/ml to 25 ng/ml or higher, more generally0.1 ng/ml to 5 ng/ml.

In addition to initial diagnosis of the βAP-related condition, themeasured concentrations of βAP may be monitored in order to follow theprogress of the disease, and potentially follow the effectiveness oftreatment (when such treatments become available). It would be expectedthat levels of βAP would decrease with an effective treatment regimen.

In vitro monitoring of βAP levels in conditioned culture medium from asuitable cell culture may be used for drug screening. By growing cellsunder conditions which result in the accumulation of βAP in theconditioned culture medium, and exposing the cultured cells to testcompounds, the effect of these test compounds on βAP production may beobserved. It would be expected that test compounds which are able todiminish the amount of βAP accumulation would be candidates for testingas inhibitors of βAP generation. Suitable cell lines include human andanimal cell lines, such as the 293 human kidney cell line, humanneuroglioma cell lines, human HeLa cells, primary human endothelialcells (e.g. HUVEC cells), primary human fibroblasts or lymphoblasts,primary human mixed brain cells (including neurons, astrocytes, andneuroglia), Chinese hamster ovary (CHO) cells, and the like.

Preferred for use in drug screening methods according to the presentinvention are cell lines capable of expressing APP variants whichoverproduce βAP. By "overproduce," it is meant that the amount of βAPproduced from the variant APP will be greater than the amount producedfrom any or all of the normal APP isoforms, e.g., the 695, 751, and 770amino acid isoforms which have been previously described. Particularlypreferred are APP variants having one or several amino acidsubstitutions directly amino-terminal of the βAP cleavage site. Forexample, as shown in the Experimental section herein, K293 cells whichexpress an APP DNA bearing a double mutation (Lys⁵⁹⁵ →Asn⁵⁹⁵ and Met⁵⁹⁶→Leu⁵⁹⁶) found in a Swedish FAD family produce approximatelysix-to-eightfold more βAP than cells expressing normal APP. The mutationat residue 596 appears to be principally responsible for the increase.

Similarly, in vivo monitoring of βAP in animal models, such as the mouseanimal model disclosed in WO 91/19810, the disclosure of which isincorporated herein by reference, and animal models expressing other APPisotypes and/or variants, may also be used to screen compounds fortherapeutic effectiveness (usually for testing of compounds which havepreviously been identified by an in vitro screen, such as the in vitroscreen described above). The test compound(s) are administered to theanimal and the level of βAP or βAP fragment in a body fluid observed.Test compounds which reduce the level of the βAP in certain body fluidsare considered to be candidates for further evaluation.

The test compounds can be any molecule, compound, or other substancewhich can be added to the cell culture without substantially interferingwith cell viability. Suitable test compounds may be small molecules,biological polymers, such as polypeptides, polysaccharides,polynucleotides, and the like. The test compounds will typically beadministered to the culture medium at a concentration in the range fromabout 1 nM to 1 mM, usually from about 10 μM to 1 mM. Test compoundswhich are able to inhibit generation, accumulation, or secretion of βAPare considered as candidates for further determinations of the abilityto decrease βAP production in cells and/or animals.

The present invention further comprises methods for inhibiting β-amyloidproduction in cells, where the method includes administering to thecells compounds selected by the method described above. The compoundsmay be added to cell culture in order to inhibit βAP production by thecultured cells. The compounds may also be administered to a patient inorder to inhibit the deposition of amyloid plaque associated withAlzheimer's and other βAP-related diseases.

The present invention further comprises pharmaceutical compositionsincorporating a compound selected by the above-described method andincluding a pharmaceutically acceptable carrier. Such pharmaceuticalcompositions should contain a therapeutic or prophylactic amount of atleast one compound identified by the method of the present invention.The pharmaceutically acceptable carrier can be any compatible, non-toxicsubstance suitable to deliver the compounds to an intended host. Sterilewater, alcohol, fats, waxes, and inert solids may be used as thecarrier. Pharmaceutically acceptable adjuvants, buffering agents,dispersing agents, and the like may also be incorporated into thepharmaceutical compositions. Preparation of pharmaceutical conditionsincorporating active agents is well described in the medical andscientific literature. See, for example, Remington's PharmaceuticalSciences, Mack Publishing Company, Easton, Pa., 16th Ed., 1982, thedisclosure of which is incorporated herein by reference.

The pharmaceutical compositions just described are suitable for systemicadministration to the host, including both parenteral, topical, and oraladministration. The pharmaceutical compositions may be administeredparenterally, i.e. subcutaneously, intramuscularly, or intravenously.Thus, the present invention provides compositions for administration toa host, where the compositions comprise a pharmaceutically acceptablesolution of the identified compound in an acceptable carrier, asdescribed above.

Frequently, it will be desirable or necessary to introduce thepharmaceutical compositions directly or indirectly to the brain. Directtechniques usually involve placement of a drug delivery catheter intothe host's ventricular system to bypass the blood-brain barrier.Indirect techniques, which are generally preferred, involve formulatingthe compositions to provide for drug latentiation by the conversion ofhydrophilic drugs into lipid-soluble drugs. Latentiation is generallyachieved through blocking of the hydroxyl, carboxyl, and primary aminegroups present on the drug to render the drug more lipid-soluble andamenable to transportation across the blood-brain barrier.Alternatively, the delivery of hydrophilic drugs can be enhanced byintra-arterial infusion of hypertonic solutions which can transientlyopen the blood-brain barrier.

The concentration of the compound in the pharmaceutical carrier may varywidely, i.e. from less than about 0.1% by weight of the pharmaceuticalcomposition to about 20% by weight, or greater. Typical pharmaceuticalcomposition for intramuscular injection would be made up to contain, forexample, one to four ml of sterile buffered water and one μg to one mgof the compound identified by the method of the present invention. Thetypical composition for intravenous infusion could be made up to contain100 to 500 ml of sterile Ringer's solution and about 1 to 100 mg of thecompound.

The pharmaceutical compositions of the present invention can beadministered for prophylactic and/or therapeutic treatment of diseasesrelated to the deposition of βAP, such as Alzheimer's disease, Down'ssyndrome, and advanced aging of the brain. In therapeutic applications,the pharmaceutical compositions are administered to a host alreadysuffering from the disease. The pharmaceutical compositions will beadministered in an amount sufficient to inhibit further deposition ofβAP plaque. An amount adequate to accomplish this is defined as a"therapeutically effective dose." Such effective dose will depend on theextent of the disease, the size of the host, and the like, but willgenerally range from about 0.01 μg to 10 mg of the compound per kilogramof body weight of the host, with dosages of 0.1 μg to 1 mg/kg being morecommonly employed.

For prophylactic applications, the pharmaceutical compositions of thepresent invention are administered to a host susceptible to theβAP-related disease, but not already suffering from such disease. Suchhosts may be identified by genetic screening and clinical analysis, asdescribed in the medical literature (e.g. Goate (1991) Nature349:704-706). The pharmaceutical compositions will be able to inhibit orprevent deposition of the βAP plaque at a symptomatically early stage,preferably preventing even the initial stages of the β-amyloid disease.The amount of the compound required for such prophylactic treatment,referred to as a prophylactically-effective dosage, is generally thesame as described above for therapeutic treatment.

The following examples are offered by way of illustration, not by way oflimitation.

EXPERIMENTAL Materials and Methods 1. Antibody Preparation

a. Monoclonal Antibodies to the βAP Junction Region.

Monoclonal antibodies to the junction region of βAP were prepared usinga synthetic peptide spanning amino acid residues 13-28 (βAP₁₃₋₂₈).βAP₁₃₋₂₈ was conjugated to an immunogen (α-CD3ε antibody; Clone No.145-2C11, Boehringer-Mannheim) usingm-maleimidobenzoyl-N-hydroxysuccinimide ester (MBS) according to themanufacturer's (Pierce) instructions.

A/J mice were immunized initially intraperitoneally (IP) with the βAPconjugate mixed with complete Freund's adjuvant. Fourteen days later,the mice were boosted IP with the βAP conjugate mixed with phosphatebuffered saline (PBS) at 14 day intervals. After six total boosts, themice were finally boosted intravenously with HAP conjugate mixed withPBS and fused 3 days later. Fusion of spleen cells with P3,653 myelomacells was performed according as described in Oi and Herzenberg,Selective Methods in Cellular Immunology, Mishell and Shigii, Eds., W.H. Freeman and Company, San Francisco, Chapter 17 (1980). Serum titersand initial screens were performed by the RIA method described below.Several clones were expanded to a 24 well plate and subjected to furtheranalysis as described below. Clones of interest were produced in mouseascites.

The RIA method used to screen serum bleeds and fusion hybridomasupernatants was based upon a method developed by Wang et al. (1977) J.Immunol. Methods 18:157-164. Briefly, the supernatant (or serum) wasincubated overnight at room temperature on a rotator with ¹²⁵ I-labeledβAP₁₋₂₈ and Sepharose® 4B beads to which sheep anti-mouse IgG had beencoupled via cyanogen bromide. The beads from each well were harvestedonto glass fiber filter discs with a cell harvester and washed severaltimes with PBS. The filter discs were then transferred to gamma tubesand the bound radioactivity was counted in a gamma counter.

All hybridomas were tested for binding to βAP₁₋₂₈ using the methoddescribed above in the initial screen, and then retested 3 days later.βAP₁₋₂₈ positive clones were further characterized for reactivity to ¹²⁵I-labeled βAP₁₋₁₆ using the RIA method described above. No clones werefound to bind βAP₁₋₁₆. In a peptide capture ELISA, all clones were foundto react with βAP₁₃₋₂₈ while no clones reacted to βAP₁₇₋₂₈. Therefore,it was determined that all clones had an epitope within the junctionregion spanning amino acids 16 and 17.

Based on results of the above assays, several clones were expanded into24 well plates. These clones were further characterized by saturationanalysis. Supernatants at the 50% titer point (as determined by the RIAmethod described above) were added to wells containing Sepharose®-sheepanti-mouse IgG beads, a constant amount of ¹²⁵ I-labeled βAP₁₋₂₈, andvarying amounts of unlabeled βAP₁₃₋₂₈ or βAP₁₇₋₂₈. The concentration ofcold peptide for 50% inhibition was determined for each antibody. Forthe βAP₁₇₋₂₈, no inhibition was seen at 100 ng/well for any clones. The50% inhibition point for βAP₁₃₋₂₈ ranged from 10-80 ng/well. The cloneswere also characterized based on reactivity in Western blots. Based ontiter point, sensitivity (as determined by the 50% inhibition point),and reactivity on Western blot, several clones were produced in ascites.

Antibodies from hybridomas designated 067, 266, 297, and 361 wereselected for use as a capture antibody in the assays described below.

b. Monoclonal Antibodies to the N-terminal Region of βAP.

Monoclonal antibodies to the N-terminal region of βAP were preparedusing a synthetic peptide spanning amino acid residues 1-28 (βAP₁₋₂₈).βAP₁₋₂₈ was chemically coupled using disuccimidyl suberate (DSS) torabbit serum albumin (RSA) using a 20:1 molar ratio of peptide toprotein in 50 mM sodium phosphate, pH 7.0, 150 mM NaCl, overnight at 21°C. using 1 mM DSS (Hyman et al. (1992) J. Neuropath. Exp. Neuro. 51:76).

Antibodies 10D5 and 6C6 were obtained from a fusion where mice hadreceived 5 injections of βAP₁₋₂₈ coupled to RSA via DSS at 100 μg/ml.The initial injection was in complete Freund's adjuvant (CFA) followedby second and subsequent injections in incomplete Fruend's adjuvant(IFA) every 10-14 days. Three days before the fusion, mouse 4 which hada titer of 1/70,000 as measured by ELISA against βAP₁₋₂₈, received 100μg of βAP₁₋₂₈ RSA in PBS intraperitoneally as a final boost. Screeningwas done by ELISA and on paraffin-fixed AD brain sections. The coatingconcentration of βAP₁₋₂₈ was 1 μg/well. 10D5 and 6C6 were positive byELISA and AD brain tissue section.

Antibodies from hybridomas designated 10D5 and 6C6 were selected for useas a reporter antibody in the assays described below.

c. Polyclonal Antibodies.

Polyclonal antibodies were raised against synthetic peptides βAP₁₋₃₈,βAP₁₋₄₀, and βAP₁₋₄₂, and were designated anti-βAP₁₋₃₈ (antiserum Y),anti-βAP₁₋₄₀ (antiserum 1280) and anti-βAP₁₋₄₂ (antiserum HM). Rabbitswere immunized with 0.5-3.0 mg of one of these peptides (unconjugated)in complete Freund's adjuvant intradermally. The rabbits receivedbooster injections of 0.1-0.5 mg peptide 3 weeks after primaryimmunization and at approximately 2-4 week intervals thereafter untilhigh titers of anti-peptide reactivity could be detected in samples ofthe rabbit serum. These antisera were then used in immunological assaysat dilutions ranging from 1:300 to 1:1,500.

2. ELISA Assay

a. Binding of Capture Antibody to Microtiter Wells.

Monoclonal antibody 266 was diluted to a concentration of 5 μg/ml, andmonoclonal antibody 067 to 10 μg/ml in a buffer containing NaH₂ PO₄.7H₂O, 26.2 g/L; NAN₃, 1 g/L; pH 8.3. One hundred μl/well of this solutionwas then dispensed in a 96 well polystyrene transparent COSTAR plate andincubated overnight at room temperature. Following coating, theremaining solution was aspirated and the non-specific antibody bindingsites were blocked with 0.25% human serum albumin (HSA) dissolved in abuffer containing NaH₂ PO₄.H₂ O, 1 g/L; Na₂ HPO₄.7H₂ O, 10.8 g/L; NaN₃,0.5 g/L and sucrose, 25 g/L; pH 7.4. These coated/blocked plates wereused immediately or dried in a desiccator and stored in a dry containerat 4° C. for a maximum of 5 days.

b. Assay Protocol.

Calibrators containing known amounts of βAP and samples from variousbodily or extra bodily fluids were then added to the plate at 100μl/well. The samples were added undiluted or diluted in a buffercontaining NaH₂ PO₄.H₂ O, 0.2 g/L; Na₂ HPO₄.7H₂ O, 2.16 g/L; NaN₃, 0.5g/L; BSA (globulin free) 6 g/L; Triton X-405, 0.5 mL/L; NaCl, 8.5 g/L;pH 7.4. Samples and calibrators were incubated in the wells for 1 hourat room temperature, subsequently aspirated, and the wells washed with300 μl/well of a solution containing NaCl, 80 g/L; KCl, 3.8 g/L; Trisbase, 5.85 g/L; Tris HCl, 31.75 g/L; and 0.05% Tween® 20; pH 7.5 (TBS).

NHS-biotin (15 mg) was dissolved in 0.25 ml dimethylsulfoxide, and 10 μlof this solution was added to 1 mg of 10D5 or 6C6 antibody suspended in1 ml of sodium carbonate solution, 50 mM, pH 8.5. The mixture wasincubated in the dark for 11/2 hours at room temperature and thendialyzed against phosphate buffered saline, pH 7.4 for 48 hours at 4°C., to produce biotinylated reporter antibody. One hundred μl/well ofthe biotinylated reporter antibody (10D5 or 6C6) diluted to 3 μg/ml wasthen added to each well and incubated for another hour at roomtemperature. The antibody diluent consisted of Trizma base, 1.21 g/L;NaCl, 29.22 g/L; NaN₃, 1.5 g/L, Triton X 405, 0.5 ml/L; PEG (Mw 3350),40 g/L; Mg Cl₂.6H₂ O, 0.095 g/L; ZnCl₂, 0.014 g/L; fetal bovine serum100 ml/L; and BSA 2.5 g/L, pH 7.4.

After 1 hour incubation at room temperature with the reporter antibody(10D5 or 6C6) the supernatant was aspirated and the wells were washedthree times with 300 μl/well of TBS. Streptavidin alkaline phosphatase(100 μl/well, diluted 1:2000 in the conjugate diluent buffer) was addedand incubated for another hour at room temperature. The supernatant wasthen aspirated and washed 3 times with 300 μl/well TBS. Fluorescentsubstrate (4-methyl-umbellipheryl phosphate in 2-amino-2-methylpropranolol buffer; pH 9.5; (100 μl/well) was added) and fluorescenceread and expressed as relative fluorescent units (FSU) after 15 minutesusing a Cytofluor 2300 from Millipore, with 360/40 excitation filter and460/40 emission filter.

3. Cultured Cells

Human cells (and cells from other mammals) were cultured under standardcell culture conditions in plastic dishes or multi-well microtiterplates. In particular, human embryonal kidney carcinoma 293 cells(hereinafter designated K293 cells) were grown in Dulbecco's modifiedEagle's medium (DMEM) containing 10% fetal calf serum and antibiotics.K293 cells that had previously been transfected with a recombinant DNAconstruct containing the full coding region of the β amyloid precursorprotein (APP) were utilized in addition to untransfected K293 cells(Selkoe et al. (1988) Proc. Acad. Sci. USA 85:7341-7345; and Oltersdorfet al. (1990) J. Biol. Chem. 265:4492-4497). The transfected cellsexpress high levels of the APP protein, compared to the usual backgroundlevels of endogenous APP characteristic of K293 cells.

Several other cell types were also cultured, including human umbilicalvein endothelial cells (HUVEC); a human megakaryocytoid leukemic cellline designated DAMI; Chinese hamster ovary (CHO) cells, primary humanfibroblasts, and primary mixed brain cell cultures (including neurons,astrocytes, and microglia) established from human or rodent brain.

These various cell lines were grown at 37° C. in a tissue cultureincubator containing an atmosphere of 95% oxygen and 5% carbon dioxide.The cells were routinely subcultured by providing fresh culture mediumat regular intervals. The extracellular fluid surrounding the cells(conditioned medium) was harvested from cells grown either understandard resting conditions or following various biochemical treatmentsof the cells. All cultured cells and their derived media samples werehandled under aseptic conditions.

Cultures of human-mixed brain cells for use in immunoaffinitychromatography studies were prepared as follows. Fetal neural tissuespecimens were obtained from 12-14 week old fetal cadavers. Samples ofcerebral cortex were rinsed twice with Hank's Balanced Saline solution(HBSS). Cortical tissue (2-3 grams) was placed in 10 mls of cold HBSS towhich 1 mg of DNase (Sigma Chemical Co., St. Louis, Mo. D3427) wasadded. The triturated suspension was filtered through Nitex nylonscreens of 210 μm then 130 μm, as described by Pulliam et al. (1984) J.Virol. Met. 9:301.

Cells were harvested by centrifugation and resuspended in neuronalmedium (MEM fortified with 10% fetal bovine serum, 1% glucose, 1 mM Napyruvate, 1 mM glutamine, 20 mM KCl). Polyethyleneimine coated 100 mmdishes were seeded with 1.5×10⁷ cells in 8 mls of neuronal medium. Themedium was harvested and fresh medium added twice weekly. Theconditioned medium from the cells (HFBC-CM) was frozen until use.

4. Immunoprecipitation/Autoradiography Assay for βAP

a. Metabolic Labeling and Immunoprecipitation.

K293 cells grown under standard culture conditions underwent metaboliclabeling of newly synthesized proteins by addition of ³⁵ S-radiolabeledmethionine to the culture medium. During this step, the medium containedno unlabeled ("cold") methionine but was otherwise identical to thestandard medium used to culture K293 cells. Amounts of radioactivemethionine varying from 50-300 μCi/ml of media were used in the labelingexperiments. Cells were incubated for approximately 10-20 hours.Thereafter, the medium containing any radiolabeled proteins releasedfrom the cell was collected.

A polyclonal antibody produced to a synthetic βAP peptide comprising theamino acids Asp-1 through Val-40 (βAP₁₋₄₀) was added to the collectedmedia and incubated for periods varying from 2-10 hours. This allowedantigen-antibody complexes to form between the anti-βAP antibody and anyβAP peptide present in the culture media. Thereafter, a proteinA-Sepharose® reagent capable of binding to immunoglobulins (antibodies)was added, and this mixture was further incubated for varying periods of2-10 hours. This incubation enabled the protein A-Sepharose® beads tobind to the anti-βAP antibodies which in turn were bound to βAP peptide.The conditioned media was then centrifuged at 12,000 xg for 10 minutesto pellet the antigen-antibody-protein A-Sepharose® bead complexes.

b. SDS-Polyacrylamide Gel Electrophoresis (PAGE) of theImmunoprecipitate.

The immunoprecipitates of the media from metabolically labeled cells waselectrophoresed on 10-20% Tristricine gels, which have the advantage ofresolving low molecular weight proteins (such as βAP) well. The gelswere then dried and exposed to X-ray film to produce an autoradiogram orfluorogram. Exposure times varied but were usually in the range of 2-7days. Following development of the X-ray film, any radiolabeled proteinsthat were precipitated from the cell media by the anti-βAP antibody werevisualized as dark bands at the appropriate molecular weight (i.e., 4kD).

5. Preparation of 266 Resin

Antibody 266 (15 mls at 0.85 mg/ml) was dialyzed versus 10 mM Naacetate, 15 mm NaCl, pH 5.5 and then coupled to Affi-Gel® Hz Hydrazide(Bio-Rad, Richmond, Calif.) according to the manufacturer's protocol,using approximately 5 mls of resin. One ml of the resin was placed in a1×10 cm column for the purification of βAP from 4 liters of conditionedmedium.

6. Western Blotting

Samples were subjected to SDS-PAGE on 10%-20% Tricine gels (Novex) andtransferred to PVDF membranes (Problot, Applied Biosystems) at 40 volts,overnight, in the buffer system described by Towbin, et al. (1979) Proc.Natl. Acad. Sci. USA 76:4350-4354. Visualization of immunoreactiveproteins employed the TROPIX chemiluminescence system according to themanufacturer's directions for the AMPPD substrate. The primary antibodyused was 10D5 at a concentration of 5 μg/ml.

7. Construction and Analysis of the `Swedish` FAD Mutation

The Swedish mutation involves two adjacent base pair conversions:nucleotide 1785 G to T and nucleotide 1786 A to C which leads to twoamino acid exchanges: Lys→Asn⁵⁹⁵ and Met→Leu⁵⁹⁶ (all numbering based onAPP₆₉₅).

To analyze the biochemical effect of this mutation on the metabolism ofAPP in vitro it was introduced by in vitro mutagenesis in an expressionvector for eukaryotic expression of APP molecules (described in Selkoeet al., 1988 supra). In this case, both forms of the vector carrying the695 and the 751 amino acid forms of APP were used. Mutagenesis wasperformed by use of two oligonucleotide primers derived from the APPsequence and polymerase chain reaction (PCR). Primer 1 (sense) is a30-mer and has the sequence GAG GAG ATC TCT GAA GTG AAT CTG GAT GCA (SEQID No.:3). This primer contains a BglII restriction endonuclease site(AGA TCT) corresponding to the BglII site in position 1770 of APP andcontains the two described nucleotide exchanges at positions 24 and 25of the primer. Primer 2 (anti-sense) is a 29-mer with the sequence AATCTA TTC ATG CAC TAG TTT GAT ACA GC (SEQ ID No:4). The primer contains aSpeI restriction endonuclease site (ACT AGT) corresponding to position2360 of APP. Using a normal APP cDNA for a template, the two primersallow the creation of a DNA fragment of approximately 600 basepairs inlength by standard PCR (reagents and protocols from Perkin Elmer). Theobtained fragment as well as the expression vector containing the normalAPP cDNA were cleaved with restriction endonucleases BglII and SpeI.

BglII and SpeI were chosen as they are both single cut sites in thisvector and therefore allow the simple removal of the non-mutatedrestriction fragment corresponding to the fragment created by PCR.Accordingly the approximately 600 basepair vector fragment was replacedby the PCR generated fragment of equal length carrying the mutation bystandard techniques. DNA of recombinant bacterial clones was obtained bystandard methods which was screened for the absence of an Mbo IIrestriction endonuclease site. Then the DNA sequence was confirmed bysequencing of the complete region that had undergone the PCR reaction.

In addition to the construction of the double mutation, the effects ofeach of the two mutations were separately examined. Using appropriateprimers or olignucleotides specific for either the 595 Lys→Asnsubstitution or the 596 Met→Leu substitution, DNA constructs wereprepared and used to transfect K293 cells as described.

Analysis of the effects of the mutation was carried out by transientexpression of the obtained mutated clone in 293 cells. The DOTAP reagenttransfection method was used according to the manufacturer'sspecifications (Boehringer Mannheim, Indianapolis, Ind.). Conditionedmedium was harvested 48 hours after transfection. Transfectionefficiency was assessed by a sandwich ELISA for APPs in the conditionedmedium with affinity purified polyclonal antibodies B5 (biotinylated) toa bacterial fusion protein of APP₄₄₄₋₅₉₂ and the capture antibody B3, toa bacterial fusion protein of APP₂₀₋₃₀₄. βAP levels were measured by theELISA described above in Example 2. As described below, the measurementof βAP in the conditioned media of transiently transfected K293 cellsexpressing the Swedish variant form of APP shows a 6-7 fold increase inproduction of βAP.

Results

The βAP ELISA assay was used to detect known amounts of synthetic βAPpeptides βAP₁₋₃₈ and βAP₁₋₄₀. The assay employing 266 capture antibodyand 10D5 reporter antibody was able to detect the peptides at 0.1 ng/ml.See FIG. 1. Moreover, the 266/10D5 assay was found not to significantlycross-react with full length APP, secreted APP 695 or 751, recombinantAPP fragments constructs 15 or 6, βAP fragments 15-20, 11-18, 13-18, or13-20, or fibrinogen (Table I).

                  TABLE I                                                         ______________________________________                                        βAP Cross-Reactivity in 266/l0D5 ELISA                                   Molecule        ng/ml   % Cross-Reactivity                                    ______________________________________                                        Full Length APP 1-100   0                                                     Secreted APP 695                                                                              1-100   0                                                     Secreted APP 751                                                                              1-100   0                                                     Construct 15*   1-100   0                                                     Construct 6**   1-100   <0.1                                                  βAP Fragment 15-20                                                                       1-1000  0                                                     βAP Fragment 11-18                                                                       1-1000  0                                                     βAP Fragment 13-18                                                                       1-1000  0                                                     βAP Fragment 13-20                                                                       1-1000  0.2                                                   Fibrinogen Type I                                                                             1-1000  0                                                     Fibrinogen Type II                                                                            1-1000  0                                                     Fibrinogen Type III                                                                           1-1000  0                                                     ______________________________________                                         *Described in Sinha et al. (1991) J. Biol. Chem. 266:2104-21013.              **Residues 590-695, as numbered in 695 isoform.                          

The ELISA assay was used to screen blood and CSF samples from humans,dogs, guinea pigs, and rats. Detectable amounts of βAP were found, withconcentrations in the ranges set forth in Table II.

                  TABLE II                                                        ______________________________________                                        βAP Level in Plasma and CSF of Various Species                           Species   CSF βAP (ng/ml)                                                                          Plasma βAP (ng/ml)                             ______________________________________                                        Human     0.1-20.0         0.1-30.0                                           Dog       2.0-10.0        2.0                                                 Guinea Pig                                                                              2.5-8.0         4.0-5.0                                             Rat       1.5             ND                                                  Rabbit    1.5-9.0         0.5-3.0                                             ______________________________________                                    

A comparative study was carried out in groups of normal individuals andAD patients, both in plasma and CSF. Samples were screened using theELISA assay, with the results for plasma set forth in FIG. 2A and theresults for CSF set forth in FIG. 2B. βAP levels in CSF for normalindividuals (C), AD patients, cerebrovascular accident (CVA), andParkinson's Disease (PD) are set forth in FIG. 3, where the horizontalline in each group represents the average βAP level for that group. ACSF pool of approximately 1000 individuals had a mean value of 2.5 ng/mlin CSF, circled in FIG. 3, row C. The rest of the control individualshad a variety of non-AD neuronal degenerative diseases. The AD meanvalues are well above the control pool value.

A number of transfected and non-transfected cultured cells were testedfor release of βAP using the ELISA assay. All cells tested were found torelease βAP into the culture medium, with the APP transfected cellsreleasing higher concentrations than released from non-transfectedcultured cells, as set forth in Table III.

                  TABLE III                                                       ______________________________________                                        Release of βAP by Cells in Culture                                       Cell Type      Transfection                                                                             βAP (mg/ml)                                    ______________________________________                                        K293           --         0.1-0.4                                             K293           695        1.6-2.5                                             K293           751        1.2-2.5                                             Mixed brain cells                                                                            --         4.0                                                 CHO            751        2.0-9.0                                             ______________________________________                                    

Using the immunoprecipitation/autoradiography assay described above inExample 4, it was shown that polyclonal antibody 1280 immunoprecipitateda 4 kD protein from K293 cell media that comigrated precisely with astandard sample of radioiodinated synthetic βAP₁₋₄₀ peptide. Inaddition, a 3 kD protein was simultaneously precipitated. This appearsto be a fragment of βAP lacking the first 10 or 16 amino acids. When the1280 antibody was preabsorbed with synthetic βAP₁₋₄₀ peptide to blockits activity, no 3 kD or 4 kD bands were precipitated from the K293 cellmedia. When the conditioned medium of K293 cells overexpressing APP wascentrifuged at 100,000 xg for 2 hours (to pellet any insolubleproteinaceous material), immunoprecipitation/autoradiography with the1280 antibody showed that substantially all of the 3 kD and 4 kDproteins remained in the supernatant, (see FIG. 6). This experimentdemonstrates the βAP found in culture media is a soluble molecule, incontrast to previous reports about βAP in postmortem human brain tissue(see for example, Glenner and Wong (1984), supra).

The precipitation of the 4 kD βAP comigrating peptide from the media ofK293 cells transfected with βAPP cDNA was confirmed by utilizingadditional βAP antibodies. Antibody Y to synthetic βAP₁₋₃₈ peptideprecipitated the 4 kD protein in identical fashion to antibody 1280.Also, antibody HM to synthetic βAP₁₋₄₂ precipitated the 4 kD protein. Asa control, each of these antibodies was preabsorbed with its syntheticpeptide antigen, thereby neutralizing its activity. Thereafter, theantibodies no longer immunoprecipitated the 4 kD βAP peptide fromconditioned media. As an additional control, the preimmune sera (i.e., asample of normal serum taken from each rabbit used to raise thepolyclonal antibodies prior to the actual immunization) did notimmunoprecipitate the 4 kD peptide from the media.

To ascertain the immunochemical specificity of the 4 kD βAP comigratingpeptide precipitated from media, other antibodies to regions of APPflanking the βAP region were used in the aboveimmunoprecipitation/autoradiography assay. For example, an antibody tothe 20-amino acid region immediately amino-terminal to the beginning ofthe βAP region of APP failed to precipitate the 4 kD peptide from media.Likewise, an antibody to the last 20 amino acids at the carboxylterminus of APP (60 amino acids beyond the βAP region) also failed toprecipitate the 4 kD peptide. In contrast, an antibody to the first 15residues of βAP successfully precipitated the 4 kD band. Likewise,antibodies to the middle portion of βAP also precipitated the 4 kDpeptide, but not the 3 kD peptide discussed above. These variousantibody precipitations demonstrate that the 4 kD peptide present in themedia of cultured cells (e.g., K293 cells) shows the specificimmunochemical reactivities characteristic of βAP. The 3 kD peptide inthe media shows the specific immunochemical reactivity of βAP lackingthe first 10 or 16 residues. Evidence that the antibodies were active ineach reaction was provided by the co-precipitation from the same mediaof the normal secreted fragment of APP (designated "soluble APP" or"APPs") whenever the precipitation reactions were carried out withantibodies to that region of APP. This large soluble APP fragment isknown to be present normally in the media of cultured cells expressingAPP. Its coprecipitation by anti-βAP antibodies thus represents apositive control reaction demonstrating the intact activity of theantibodies used in this assay.

As an additional control reaction to demonstrate that theimmunoprecipitated 4 kD protein comigrating with synthetic βAP indeedrepresented authentic βAP, the media of cells transfected with an APPcDNA (and thus overexpressing APP) were compared to the media ofuntransfected cells. Immunoprecipitation/autoradiography showed anincreased amount of precipitable 4 kD protein in the media of thetransfected versus non-transfected cells, as expected from theirincreased production of the APP precursor molecule. See FIG. 5.Similarly, the media of the transfected cells showed more of the APP_(s)soluble fragment of APP than the media of the non-transfected cells;this positive control reaction was observed simultaneously in theimmunoprecipitates that contained the 4 kD protein.

The same result was obtained when a different cell type, chinese hamsterovary (CHO) cells, was used. Comparison of CHO cells eitheruntransfected or transfected with APP cDNA showed increased levels ofthe 4 kD 1280-precipitable peptide in the media of the latter cells.These results provided further evidence that the 4 kD protein in thecell media was bona fide βAP.

Authentic, native βAP was extracted from autopsied human cerebral cortexof patients who died with AD. This sample of Aβ from AD brain tissuecomigrated with the 4 kD 1280-precipitable peptide from cultured cellmedia when analyzed by SDS-polyacrylamide gel electrophoresis. Thiscomigration provided further support for the identity of the 4 kDpeptide as βAP.

Four liters of human fetal brain culture-conditioned media (HFBC-CM)were thawed and filtered through a 0.45 μm filtering flask. Leupeptin (1μg/ml) and PMSF (35 μg/ml) taken from a 35 mg/ml stock in isopropanolwere added to the HFBC-CM immediately prior to affinity chromatography.The material was run through the 266-affinity column at a flow rate ofapproximately 2 ml/min at 4° C. The column was then washed with 500 mlsof PBS. Elution of material specifically bound to the resin was achievedwith 0.2M glycine pH 2.0. A total of 9 mls was used.

The eluted material was subjected to two steps of reversed phase liquidchromatography using a Vydac C4 [0.21×15 cm] reversed phase column and asolvent system containing 0.1% TFA in buffer "A" and 0.1% TFA/80%acetonitrile in buffer "B". The affinity-purified material was loadedonto the reversed phase column at 200 μl/min and then washed with 80%buffer (A) and 20% buffer "B" at 200 μl/min for 60 min and 50 μl/min for42 min to equilibrate the column and stabilize the baseline. A gradientfrom 20% to 70% "B" was executed over 50 min at 50 μl/min, and theeluant was monitored at 0D₂₂₀. Fractions of 100 μl were collected andassayed by both Western blot and ELISA. Based on these results,fractions 11 and 12 were pooled and rechromatographed under nearlyidentical conditions except that a 150 min gradient from 10 to 40% "B"was employed followed by a 20 min gradient from 40 to 100% "B".

Fraction 77 from the second reversed phase chromatography step was foundto be reactive against the 10D5 antibody by both Western blot (FIG. 4)and ELISA.

An aliquot of the material in fraction 77 was microsequenced and shownto have the N-terminal sequence of βAP, beginning with Asp.Microsequencing was performed on an Applied Biosystems Model 477 proteinsequencer using a microscale reaction cartridge and Applied Biosystems'sMICFST program cycles.

A second aliquot was subjected to electrospray ionization massspectrometry, performed at M-SCAN, Inc., revealing a mass peak at4329.81 (+/-1.27 SD) which would correspond to the expected mass of βAP1-40 (theoretical MW of 4330.4). N-terminal sequencing of several of theA₂₂₀ peaks was positive for βAP. The ELISA revealed the βAP sequence tobe present in fractions 65, 70, 75 in addition to the major peak infraction 77. Fractions 65 and 70 contained an additional sequence of apreviously undescribed βAP fragment beginning at βAP residue 11 (Glu).In fraction 65, sufficient material was present to sequence through βAPresidue 33.

Western Blot (FIG. 4) of RPLC fractions of 266-affinity purifiedmaterial from HFBC-CM. 3 μl of the indicated fractions were diluted with15 μl of SDS-PAGE sample buffer and neutralized with 1 μl of 1M NaOHbefore boiling and processing as described above. The material loaded inthe respective lanes was as follows:

    ______________________________________                                               Lane RPLC fraction                                                     ______________________________________                                               1    65                                                                       2    70                                                                       3    71                                                                       4    74                                                                       5    75                                                                       6    77                                                                       7    78                                                                       8    79                                                                       9    83                                                                       10   84                                                                       11   85                                                                ______________________________________                                    

Lane 12 was buffer only; lane 13 contained 20 ng of βAP 1-38; lane 14contains 100 ng of βAP 1-38; lane 15 contains low molecular weightRainbow® standards (Amersham). Note the approximate 4 kD band in lane 6which co-migrates with the βAP standard in lane 14.

Parallel experiments to those described for HFBC-CM were performed using4 liters of human CSF to structurally characterize the βAPimmunoreactivity from this source. Sequencing data confirmed thepresence of N-terminal sequences beginning with βAP residue 1 (Asp) andβAP residue 11 (Glu).

The increase in βAP levels in the media of the Swedish transfectants wasquantitated using the βAP-specific ELISA with monoclonal antibodies 266and 6C6. The sandwich ELISA for APP_(S) used polyclonal antibodies B5and B3. For each ELISA, increasing amounts of purified synthetic βAP₁₋₄₀or purified APP_(S) from conditioned media of K293 cells transfectedwith cDNA for the APP 695 isoform were used to construct a standardcurve. Quantitation of βAP (left panel) and APP_(S) (right panel) inconditioned media in the transiently transfected K293 cells is shown inFIG. 7. Each column represents the mean of four transfections with theexception of the mock column, which is based on three cultures. Errorbars indicate the standard deviation. For columns without error bars,the standard deviation was less than 0.01 units.

As shown in FIG. 7, cells expressing the Swedish variant APP 695construct produced 6-7 fold more βAP in their media than identicallytransfected cells expressing normal APP (695 isoform). Moreover, asimilar 7-8 fold increase was observed in cultures expressing theSwedish mutation in the APP 751 isoform (FIG. 7). Similar increases inβAP levels were documented using a second method of quantitation:phosphor imager analysis of the 4 kD βAP band in gels of 1280immunoprecipitates. This method further demonstrated that the 3 kDfragment was decreased several fold in the media of the Swedishtransfectants. CHO and K293 cells stably transfected with cDNA theSwedish mutation in the APP 751 isoform also showed marked increases inthe levels of βAP in their cultured media.

To study the mechanism responsible for the increased βAP production, theeffects of each single mutation (Lys→Asn⁵⁹⁵ and Met-Leu⁵⁹⁶) in the APP695 isoform were separately examined. FIG. 8 shows conditioned media ofradiolabeled K293 cells transiently transfected with no DNA (lane 1);normal APP (lane 2), Swedish mutant APP 695 KM-NL (lane 3), variant APP695 K-N (lane 4), variant APP 695 M-L (lane 5), APPΔC (APP cytoplasmicdomain deletion, lane 6) and APPΔC KM-NL (Swedish mutations andcytoplasmic domain deletions, lane 7) and immunoprecipitated with 1280.The βAP and 3 kD bands are indicated by arrows. ¹²⁵ I-labeled syntheticβAP (1-40) was run as a size marker on the same gel (lane 8). Cellsexpressing the Met→Leu substitution had increased levels of βAP in theirmedium, whereas cells expressing the Lys→Asn substitution had levelssimilar to normal transfectants (FIG. 8, lanes 2-5). This findingsuggests that the 596 mutation results in more proteolytic cleavage ofAPP at the Leu-Asp peptide bond than at the normal Met-Asp bond. It ispossible that the Lys→Asn switch at 595 may further enhance the cleavagewhen coupled with the Met→Leu substitution at 596.

Cells containing the Swedish mutation together with the deletion of thecytoplasmic domain of APP deletion, thus removing the Asn-Pro-X-Tyr SEQID No:2 lysosomal targeting consensus sequence, still producedsubstantially more βAP in their media than normal transfectants butshowed increased levels of the 3 kD peptide (FIG. 8, lanes 6 and 7).This result indicates that the effect of the Swedish mutations does notrequire an intact cytoplasmic domain and that generation of APP isunlikely to require processing of APP in late endosomes/lysosomes.

These findings provide experimental evidence that point mutations in theAPP gene found in FAD kindreds can result directly in increasedgeneration of βAP. Analysis of the Swedish mutations demonstrates theutility of measuring βAP production in vitro from APP bearing aparticular mutation (e.g., mutations at residue 717 immediatelyfollowing the βAP region and those within the βAP region) as not only aroute to elucidating the mechanism of accelerated β-amyloidosis infamilial forms of AD, but also to the utility of APP variants in themethods of the present invention.

Although the foregoing invention has been described in detail forpurposes of clarity of understanding, it will be obvious that certainmodifications may be practiced within the scope of the appended claims.

    __________________________________________________________________________    SEQUENCE LISTING                                                              (1) GENERAL INFORMATION:                                                      (iii) NUMBER OF SEQUENCES: 4                                                  (2) INFORMATION FOR SEQ ID NO:1:                                              (i) SEQUENCE CHARACTERISTICS:                                                 (A) LENGTH: 43 amino acids                                                    (B) TYPE: amino acid                                                          (C) STRANDEDNESS: single                                                      (D) TOPOLOGY: linear                                                          (ii) MOLECULE TYPE: peptide                                                   (xi) SEQUENCE DESCRIPTION: SEQ ID NO:1:                                       AspAlaGluPheArgHisAspSerGlyTyrGluValHisHisGlnLys                              151015                                                                        LeuValPhePheAlaGluAspValGlySerAsnLysGlyAlaIleIle                              202530                                                                        GlyLeuMetValGlyGlyValValIleAlaThr                                             3540                                                                          (2) INFORMATION FOR SEQ ID NO:2:                                              (i) SEQUENCE CHARACTERISTICS:                                                 (A) LENGTH: 4 amino acids                                                     (B) TYPE: amino acid                                                          (C) STRANDEDNESS: single                                                      (D) TOPOLOGY: linear                                                          (ii) MOLECULE TYPE: peptide                                                   (xi) SEQUENCE DESCRIPTION: SEQ ID NO:2:                                       AsnProXaaTyr                                                                  (2) INFORMATION FOR SEQ ID NO:3:                                              (i) SEQUENCE CHARACTERISTICS:                                                 (A) LENGTH: 30 base pairs                                                     (B) TYPE: nucleic acid                                                        (C) STRANDEDNESS: single                                                      (D) TOPOLOGY: linear                                                          (ii) MOLECULE TYPE: DNA (primer)                                              (xi) SEQUENCE DESCRIPTION: SEQ ID NO:3:                                       GAGGAGATCTCTGAAGTGAATCTGGATGCA30                                              (2) INFORMATION FOR SEQ ID NO:4:                                              (i) SEQUENCE CHARACTERISTICS:                                                 (A) LENGTH: 29 base pairs                                                     (B) TYPE: nucleic acid                                                        (C) STRANDEDNESS: single                                                      (D) TOPOLOGY: linear                                                          (ii) MOLECULE TYPE: DNA (primer)                                              (xi) SEQUENCE DESCRIPTION: SEQ ID NO:4:                                       AATCTATTCATGCACTAGTTTGATACAGC29                                               __________________________________________________________________________

What is claimed is:
 1. A method for detecting a soluble β-amyloidpeptide (βAP) in a fluid sample in the presence of β-amyloid precursorprotein (APP) or fragments thereof, said method comprising:capturingsoluble βAP from the sample using a first binding substance underconditions in which the first specific binding substance binds to anepitope at a junction region on the βAP and which is substantially freefrom cross-reactivity with APP and fragments thereof other than βAP,wherein the junction region is centered at the site between βAP aminoacid residues 16 and 17 and is a target for normal proteolytic cleavage;and detecting capture of the soluble βAP using a labeled second bindingsubstance which binds to an epitope on a second region of the solubleβAP other than the epitope on the βAP which is bound by the firstbinding substance.
 2. A method as in claim 1, wherein the βAP is intactβAP.
 3. A method as in claim 1, wherein the fluid sample is selectedfrom the group consisting of culture medium, blood, CSF, urine, andperitoneal fluid.
 4. A method as in claim 1, wherein the soluble βAP iscaptured on a solid phase, and the capture is detected by exposing thesolid phase to the labeled second binding substance and thereafterdetecting the presence of the label on the solid phase.
 5. A method fordetecting a soluble β-amyloid peptide (βAP) in a fluid sample, saidmethod comprising:exposing the sample to a first binding substancespecific for an epitope at a junction region on soluble βAP disposedbetween amino acid residues 13 to 28; and detecting binding between thefirst binding substance and the soluble βAP under conditions where thefirst binding substance binds to the βAP without substantialcross-reactivity with β-amyloid precursor protein (APP) and fragmentsthereof other than βAP.
 6. A method as in claim 5, wherein the fluidsample is selected from the group consisting of culture medium, blood,CSF, urine, and peritoneal fluid.
 7. A method as in claim 5, wherein thefirst binding substance is an antibody raised against a peptideconsisting of amino acid residues 13 to 28 of βAP.
 8. A method as inclaim 7, wherein the antibody is a monoclonal antibody.
 9. A method asin claim 5, wherein binding of the first binding substance and thesoluble βAP is detected by separating bound complexes of the bindingsubstance and βAP, exposing the separated bound complexes to a labeledsecond binding substance specific for the N-terminal region of βAP, anddetecting the presence of label on the bound complexes.
 10. A method asin claim 9, wherein the second binding substance is an antibody raisedagainst a peptide consisting of amino acid residues 1-16 of βAP.
 11. Amethod as in claim 10, wherein the antibody is a monoclonal antibody.12. A method for detecting a soluble β-amyloid peptide (βAP) in a fluidsample which may contain βAP and βAP fragments as well as solublefragments of β-amyloid precursor protein (APP) other than βAP, saidmethod comprising:exposing the fluid sample to a first binding substanceunder conditions in which the first binding substance will bind to anepitope on soluble βAP and βAP fragments but will not bind to epitopeson APP fragments which may be present in the sample; and detectingbinding between the first binding substance and the soluble βAP and βAPfragments.
 13. A method as in claim 12, wherein the fluid sample isselected from the group consisting of culture medium, blood, CSF, urine,and peritoneal fluid.
 14. A method as in claim 12, wherein the firstbinding substance binds specifically to intact βAP.
 15. A method as inclaim 12, wherein the first binding substance binds specifically to anapproximately 3 kD fragment of βAP.
 16. A method as in claim 12, whereinthe first binding substance is immobilized on a solid phase, and bindingis detected by exposing the solid phase to a labeled second bindingsubstance and thereafter detecting the presence of the label on thesolid phase.